Plastic materials have been now widely used in the production of various optical materials, particularly, spectacle lenses because of their light weight, good toughness and easiness of dyeing. The important properties required for optical materials, especially, spectacle lenses are high refractive index and high Abbe number. A high refractive index reduces the thickness of lenses, and a high Abbe number reduces the chromatic aberration of lenses. To achieve a high refractive index and a high Abbe number simultaneously, various polyepisulfide compounds which are well balanced in the refractive index and the Abbe number are recently reported (Patent Documents 1 to 3). The optical materials produced from the polyepisulfide compounds proposed in these patent documents attain a refractive index of 1.7 or higher and a high Abbe number. However, materials having a still higher refractive index have been demanded.
To meet such a demand by achieving a still higher refractive index, proposed is an optical material produced by the use of an inorganic compound having sulfur atom and/or selenium atom (Patent Document 4). To make the resultant optical material highly transparent, a prepolymerization reaction and a deaeration treatment are required in the preparation of a composition containing such an inorganic compound (Patent Documents 5 and 6). However, the prepolymerization and the deaeration increase the viscosity of the composition. Particularly, the viscosity increases drastically when an increased amount of the inorganic compound having sulfur atom and/or selenium atom is used to increase the refractive index. Therefore, the operations for cast polymerization such as filtration and casting into a mold become difficult to perform.
[Patent Document 1] JP 9-71580A
[Patent Document 2] JP 9-110979A
[Patent Document 3] JP 9-255781A
[Patent Document 4] JP 2001-2783A
[Patent Document 5] JP 2004-197005A
[Patent Document 6] JP 2004-137481A